Multiple C-H bond activation of phenyl-substituted pyrimidines and triazines promoted by an osmium polyhydride: Formation of osmapolycycles with three, five, and eight fused rings

The reactions of the hexahydride complex OsH6(P iPr3)2 (1) with 4,5-dimethyl-2,6-bis(4- methylphenyl)pyrimidine (H2Ll), 2,4,6-tris-(4-methylphenyl)-l,3,5- triazine (H4L2), and 2,4,6-triphenylpyrimidine (H4L3) have been studied. Complex 1 reacts with H2Ll to give a mixture of the metallapolycyclic derivatives OsH3(HLI)(PiPr 3J2 (2) and OsH2(L1)(PiPr 3)2 (3). Compound 2 arises from the coordination of the N3-pyrimidine nitrogen atom to osmium and the ortho-CH bond activation of the C2-bonded phenyl group. The formation of 3 involves the coordination of the N1-pyrimidine nitrogen atom to osmium and the ortho-CH bond activation of both phenyl groups. The reaction of 1 with H4L2 leads to a mixture of OsH2(H2L2)(PiPr3)2 (4) and (P'Pr3)2H2Os(L2)OsH2(PiPr 3)2 (5), containing five and eight fused rings, respectively. Complex 4 results from the coordination of the N1-triazine nitrogen atom to osmium and the ortho-CH bond activation of the phenyl groups at positions 2 and 6 of the triazine ring. Complex 5 results from the coordination of the N1 and N3 of triazine to two different metal centers along with a double ortho-CH bond activation in each proximal phenyl group. Complex 1 reacts with H4L3 to afford OsH2(H2L3)(PiPr 3)2 (6) and (PiPr3) 2H2Os(L3)OsH2(PiPr3) 2 (7), which are related to 4 and 5, respectively. Complexes 2,3,4, and 5 have been characterized by X-ray diffraction analysis. The structures prove the planarity of their cores and suggest electron derealization through the polycyclic system. Quantum chemical calculations (DFT level) on model compounds clearly indicate that the Os-C and Os-N bonds of the newly formed metallapolycycles exhibit a remarkable double-bond character that is higher for the Os-C bond, in very good agreement with the experimental findings. © 2010 American Chemical Society.Financial support from the MICINN of Spain (project numbers CTQ2008-00810, CTQ2007-67730-C02-01/BQU, and Consolider Ingenio 2010 CSD2007-00006), the Diputación General deAragón (E35), and the CAMCCG07-UCM/PPQ-2596 is acknowledged. I.F. is a Ramón y Cajal Fellow. M. M.-O. thanks the MICINN for a FPI predoctoral grant.Peer Reviewe